Two experimental studies are carried out on interacting tandem bodies in incompressible, turbulent flow and the design of a hydrodynamic water channel in which the studies are conducted is discussed. The water channel has a 1 m^2 test section, and a flow velocity up to 1 m/s. The constant cross-section design consists of a recirculating channel in a horizontal plane and a submerged blade pump (propeller) similar to the design of a wind tunnel which allows much lower power consumption than typical water channel design. The first study examined is the dynamic coupling between oscillating hydrofoils in uniform, flow. Experiments are carried out on a single, finite-span, oscillating foil, as well two and three oscillating foils in tandem. Wake modes and structures of a single oscillating foil are described and found to agree well with results from previous infinite-span foil studies. The interaction between oscillating foils is described qualitatively and it is found that the response of the downstream foils is directly related to the wake modes of the upstream foil. Furthermore, it is found that low-order, locally-linear models can approximate the coupling between two and three foils and these models should hold for a large, multi-agent system or flock of such interacting bodies. The second is a case study examining the performance and safety of aerodynamic downforce devices employed on NASCAR's Car of Tomorrow (COT) racecar. The wake interactions of a deck-mounted wing is compared to that of a spoiler and the role these interactions play in flipping and aerodynamic performance is examined using 10% scale models and particle image velocimetry to educe flow topology. It is found that the smaller time and length scale of structures in the wake of a winged car should yield more predictable handling characteristics for closely following vehicles during typical race conditions. It is also shown that, under extreme yaw (180 degrees), the winged car may be more likely to create lift due to reattached flow failing to deploy roof flaps (aerodynamic safety devices) consistently.